Medical implants for greatly varying uses are known in the art. A shared goal in the implementation of modern medical implants is high biocompatibility, i.e., a high degree of tissue compatibility of the medical product inserted into the body. Frequently, only a temporary presence of the implant in the body is necessary to fulfill the medical purpose. Implants made of materials which do not degrade in the body are to be removed again, because rejection reactions of the body may occur in the medium and long term even with highly biocompatible permanent materials.
One approach for solving the above-mentioned set of problems is to mold the implant entirely or in part from a biocorrodible material. Biocorrosion is defined in the present disclosure as microbial procedures or processes solely caused by the presence of bodily media, which result in a gradual degradation of the structure comprising the material. At a specific time, the implant, or at least the part of the implant which comprises the biocorrodible material, loses its mechanical integrity. The degradation products are resorbed by the body, small residues being tolerable.
Biocorrodible materials have been developed, inter alia, on the basis of polymers of synthetic nature or natural origin. Because of the material properties, but particularly also because of the degradation products of the synthetic polymers, the use of biodegradable polymers is still significantly limited. Thus, for example, orthopedic implants must frequently withstand high mechanical strains and vascular implants, e.g., stents, must meet very special requirements for modulus of elasticity, brittleness, and moldability depending on their design.
One promising attempted achievement provides the use of biocorrodible metal alloys for this purpose. Thus, it is suggested in German Patent Application No. 197 31 021 A1 that medical implants be molded from a metallic material whose main component is to be selected from the group of alkali metals, alkaline earth metals, iron, zinc, and aluminum. Alloys based on magnesium, iron, and zinc are described as especially suitable. Secondary components of the alloys may be manganese, cobalt, nickel, chromium, copper, cadmium, lead, tin, thorium, zirconium, silver, gold, palladium, platinum, silicon, calcium, lithium, aluminum, zinc, and iron. Furthermore, the use of a biocorrodible magnesium alloy having a proportion of magnesium greater than 90%, yttrium 3.7-5.5%, rare earth metals 1.5-4.4%, and the remainder less than 1% is known from German Patent Application No. 102 53 634 A1, which is suitable, in particular, for producing an endoprosthesis, e.g., in the form of a self-expanding or balloon-expandable stent. Notwithstanding the progress achieved in the field of biocorrodible metal alloys, the alloys known up to this point are also only capable of restricted use because of their material properties, such as strength and corrosion behavior. In particular, the relatively rapid biocorrosion of magnesium alloys and their low strength in comparison to other metallic materials causes a limitation of the field of use. A medical implant is described as an innovative approach in German Patent Application No. 10 2005 003 188.9, which comprises or contains a biocorrodible amorphous or nanocrystalline alloy. The construction of implants made of magnesium and magnesium alloys, which have an increased strength in comparison to crystalline magnesium and magnesium alloys, is thus possible. However, this advantage is typically acquired by a loss of deformability and stability under alternating load because of increased bending rigidity. This in turn greatly restricts the field of use of these alloys.